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My only other suggestion before you get a spark is to see if the colour/dimension of the cable is recognisably different from your other wiring that you can see near the consumer unit. If you are saying that it's a heavy gauge cable then I'd expect it to either go to the consumer unit, or be a spur from a nearby wall socket.
In my house, they had screwed a spur cable into a bedroom socket which went along the underneath of the skirting towards my fireplace..... It then ran upwards behind some plasterboard which was covering the original fireplace, before being chased into the plaster on the wall to a height of around six foot. The cable had previously fed a wall lamp, but previous owners had simply cut the cable back and left it. Wankers.
Its a thick, don't fucking mess with me cable.
Floor is glued and nailed down.
I'm just going to get an electrician in as I want to finish the stairs this weekend